Physicians frequently make use of catheters today in medical procedures to gain access into interior regions of the body. In some procedures, the catheter carries an energy transmitting element, which is typically a metal electrode, on its distal tip to ablate body tissues.
In such procedures, the physician must establish stable and uniform contact between the energy transmitting element and the tissue to be ablated. Upon establishing contact, the physician must then carefully apply ablating energy to the element for transmission to the tissue.
The need for precise control over the emission of ablating energy is especially critical during catheter-based procedures for ablating heart tissue. These procedures, called electrophysiology therapy, are becoming increasingly more widespread for treating cardiac rhythm disturbances, called arrhythmias. Cardiac ablation procedures typically use radio frequency (RF) energy to form a lesion in heart tissue.
The level of ablating energy can be controlled, at least in part, by using a temperature sensing element to monitor surface tissue temperatures during ablation. Because of the particular heat exchange conditions between the tissue and the metallic ablation electrode contacting it, the surface temperatures measured by the sensing element usually will not correspond with the actual maximum tissue temperature. This is because the region of hottest temperature occurs beneath the surface of the tissue, usually at a depth of about 0.5 to 1.0 mm from where the energy transmitting electrode (and the sensing element) contacts the tissue. If the power is applied to heat the tissue too quickly, the actual maximum tissue temperature in this sub-surface tissue region may exceed 100.degree. C., while the surface tissue temperature sensed by the temperature sensor is only 80.degree. C. Sub-surface micro explosions are the unintended results.
The principal objective of the invention is to provide systems and methods for monitoring and reliably controlling the application of energy to ablate body tissue, thereby providing therapeutic results in a consistent and predictable fashion.